Fluorocarbon based fluids have found widespread use in industry for solvent cleaning and solvents in aerosols for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, a vapor degreaser is employed. The conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. The part can also be sprayed with distilled solvent before final rinsing.
Azeotropic or azeotrope-like compositions are particularly desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor degreasing equipment in which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point, i.e., is azeotrope-like, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not azeotrope-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity.
The compositions of the invention may also be useful in aerosol solvent applications of cleaning or deposition of certain types of lubricants, as a dust off, freeze spray or tire inflator. As an aerosol product the material is propelled from an aerosol can using a propellant.
The art is continually seeking new fluorocarbon based mixtures which offer alternatives for the above-described applications. Currently, environmentally acceptable fluorocarbon-based materials are of particular interest because the fully halogenated chlorofluorocarbons have been implicated in causing environmental problems associated with the depletion of the earth's protective ozone layer. Mathematical models have substantiated that hydrofluorocarbons like 1,1,1,3,3-pentafluoropropane (HFC 245fa) will not adversely affect atmospheric chemistry because the contribution to stratospheric ozone depletion and global warming in comparison to the fully halogenated and chlorinated fluorocarbons species is negligible.
The art has looked towards compositions which include fluorocarbon components such as 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) and also include components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. The substitute material must also possess those properties exhibited by the prior art chlorofluorocarbons including chemical stability, low toxicity, and non-flammability.
It is accordingly an object of this invention to provide novel compositions based on 1,1,1,3,3-pentafluoropropane and chlorinated ethylenes (trans 1,2 dichloroethylene, methylene chloride, trichlorethylene, and mixtures thereof), and preferably azeotrope-like compositions, which are useful in solvent and other applications, meeting the above mentioned criteria.
The present compositions are advantageous for the following reasons. The HFC-245fa component has a zero ozone depletion potential and has reasonable solvency characteristics. The chlorinated ethylene component has good solvent properties to enable the cleaning and dissolution of flux resin and oils. Thus, when these components are combined in effective amounts, an efficient, environmentally acceptable azeotrope-like solvent results.